Thermosensitive recording media are ordinarily prepared by applying a coating solution containing a leuco dye and an color developing agent onto a substrate such as paper, synthetic paper, film, plastic and the like. Thermosensitive recording medium develops color through an instantaneous chemical reaction when heated using a thermal head, hot stamp, hot pen, laser light and the like and yields a recorded image. Thermosensitive recording media are used extensively in recording media such as facsimile devices, computer terminal printers, automatic ticket dispensers, recorders for meters, receipts at super markets and convenience stores and the like.
As the color developing agent, bisphenols, alkylphenols, novolac type phenolic resins, derivatives of aromatic carboxylic acids and metal salts thereof, hydroxybenzoic acid esters, sulfonylurea compounds, activated clay, and the like are generally used.
There's a demand from the users of thermosensitive recording media for an environment-friendly color developing agent rather than such a conventional phenol type material and the like. Then thermosensitive recording media using ascorbic acid (References 1 and 2, etc.), saccharin (Reference 3 etc.) and the like as the color developing agent has been disclosed.